About Boiler Filters
First, what is a boiler filter?
Boiler filter, also referred to as "dirt trap" or "dirt separator" is often viewed as an optional or non-essential "add-on" and is one of the most overlooked components in a typical hydronic (hot water) boiler system. The role of the filter is self-explanatory - to capture dirt particles from the system water, but the importance of its' function is under-estimated.
Rust - a hidden problem
Oxidized iron, magnetite or simply rust - can be found in nearly every heating system. Even systems with all-copper, brass and stainless steel components may have rust in them from municipal or well water. A typical system may have rust from boiler heat exchanger, circulator(s), cast iron radiators, air scoops, etc.
Why is rust an issue? Dirty water not only reduces the effectiveness of heat transfer in system water, which covertly increases the operating costs and the heating bill - it also interferes with normal operation of flow/pressure/temperature sensors in boilers, circulators and other equipment, leading to more frequent maintenance, downtime and added expenses.
Boiler filter types
Boiler filters are generally of (3) main types - magnetic, non-magnetic and combi.
Non-magnetic or screen and chamber type - are chambers with a mesh inside, where velocity of water flowing through is reduced, allowing particles to settle at the bottom of the chamber and be subsequently purged using a drain valve/plug at the bottom. A typical Y-strainer would be the most primitive example, while Spirotherm SpiroTrap is well-designed solution. Standard dirt traps are effective in removing larger particles, but are not very effective in removing small rust particles.
Magnetic - an improvement over the standard dirt traps, with a magnet implemented into the design. The magnet helps to catch small rust particles suspended in water and retain them until next maintenance. Magnetic boiler filter designs, while similar in nature, may vary greatly by manufacturer and some (such as Adey) visibly outperform others.
Combi units - as the name suggests, these are a 2-in-1 boiler filter (dirt separator) and air eliminator, combined into a single unit to reduce installation costs.
Dirt traps & boiler filters - a wise investment
While the cost of an average boiler filter varies by size, design, manufacturer, etc. - it is still a fraction of the cost of maintenance or repair and would pay itself off within a year or two at most. Most high-efficiency boiler manufacturers now require a magnetic filter to be installed in order for the warranty to apply. Cast iron boiler systems would also greatly benefit from using one.